This invention relates generally to brake control devices, and more particularly to a brake control apparatus responsive to loading conditions of railway cars.
One of the successful brake control devices for railway cars has been the well-known AB freight brake control device. However, the AB brake control is a single capacity device which applies a given brake signal to each car of a train without regard to the loading of the car. The undesirable result in a train comprised of loaded and unloaded cars is a shock or buffer effect which occurs because of inadequate braking on the loaded cars and excessive braking on the unloaded cars. Thus, a need exists for a brake control device for railway cars which applies the brakes of each individual car in accordance with the loading conditions thereof.
Many types of brake control apparatus have been heretofore known and used for automatically reducing the degree of braking on railway cars carrying a light load and thereby avoiding excessive braking on the wheels of relatively lightly loaded cars. Previous types of double capacity brake control apparatus usually comprise a so-called change-over valve device and strut cylinder for measuring the degree of load carried by a railway car according to the relative positioning of sprung and unsprung portions of the railway can undercarriage. These prior devices, sometimes referred to as empty and load brake control apparatus, have generally been relatively complicated in nature and high in cost.
Furthermore, most of the heretofore known empty and load brake control apparatus for railway cars are changed over to provide either empty or load braking, accordingly as the vehicle is empty or loaded, only while the train brake pipe pressure is increasing subsequent to a brake pipe pressure reduction to substantially zero, a condition obtained under emergency brake application and not during a full or partial service brake application.
Recognizing that railway cars are often operated partially loaded, as well as fully loaded or fully unloaded, it is the general purpose of this invention to provide brake control apparatus for railway cars which is responsive to the degree of loading in each individual car to effect proficient brake application in loaded, unloaded and partially loaded railway cars, thereby preventing the undesirable buffer effect along the train caused by uneven brake application, and which continuously senses the condition of loading during emergency and service brake application.
Another purpose of the invention is to provide brake control apparatus which may readily and economically be used in combination with existing railway brake valve devices, such as the widely used AB brake valve, without requiring changes in train operating procedure. The invention functions equally well whether the train brakes are applied by a single pressure reduction, or more typically, by staged pressure reductions.
More specifically, the present invention comprises a brake control valve interposed between a brake pipe and a brake cylinder line. The control valve includes a movable diaphragm assembly suspended therein which separates two chambers connected to the brake pressure pipe and the brake cylinder line, respectively. The diaphragm assembly is responsive to a load sensing strut cylinder mounted between the sprung and unsprung portions of the railway undercarriage to actuate other valves within the control valve in order to effect a relatively reduced braking signal for an unloaded railway car with respect to the braking signal for a loaded railway car.
A given brake pipe signal may be either reduced to effect brake actuation on an unloaded railway car, or increased to effect brake actuation on a loaded railway car. In the former case, a limiting valve may be provided between the control valve and the strut cylinder of the first embodiment of the apparatus to prevent pressure reduction below a predetermined safety level. In the latter case, a limiting valve may be provided across the strut cylinder and the control valve of the second embodiment of the invention to allow, under emergency conditions, the brakes of unloaded railway cars to be actuated to the same degree as the brakes of loaded railway cars. In both cases, the strut cylinder may be adapted to sense the degree of railway car loading, thereby enabling the apparatus to initially effect brake actuation on a partially loaded railway car as though the car were fully loaded, with final actuation effected to a lower value as though the car were unloaded. Also in the latter case, there may be provided an emergency pressure source, if desired.
In a third embodiment of the invention, the diaphragm assembly is directly responsive to hydraulic actuation by the load sensing strut cylinder. A given brake pipe signal is utilized to effect brake actuation on a loaded railway car, but is reduced to actuate the brakes on an unloaded car. If desired, the apparatus can be modified to effect brake actuation on a partially loaded car, by means of a brake pipe signal relatively greater than that required for an unloaded car. In addition, the apparatus can be provided with a means for reducing wear of the strut cylinder, if desired.